With all due respect to Commager, may I also volunteer the French Revolution? The legacy and meaning of the revolution has been debated and contested in France, sometimes violently, to this day. Francois Furet may have angrily declared that "the French Revolution is OVER" back in the 1970s, but it is still being debated, everything from the level of popular support, Louis XVI's miscalculations, they loyalty of the national guard, whether Napoleon continued the revolution or was a reactionary at heart, etc. There are even many female historians who claim that the revolution took power AWAY from women, as women had more power at Versailles than in the Directory.
Our Civil War is far from the only conflict that causes continuous controversy and debate over its legacy.
The Mexican War was just as divisive.